1) Field of the Invention
The present invention relates to a process for producing a dialkyl carbonate, and more specifically, to a process for producing a dialkyl carbonate which comprises reacting at least one member selected from the group consisting of urea and alkyl carbamate with alcohol in the presence of a high boiling point organic compound. Dialkyl carbonate is a compound useful as a raw material of diphenyl carbonate.
2) Prior Art
Japanese Patent Kokai (Laid-open) No.55-102542 describes a process for producing a dialkyl carbonate by reacting urea with alcohol. Japanese Patent Kokai (Laid-open) Nos 55-102543 and 57-26645 describe a process for producing a dialkyl carbonate by reacting alkyl carbamate with alcohol. Further, Japanes Patent Kokai (Laid-open) No. 57-175147 and WO9517369 describe catalysts for above-mentioned reaction.
In known conventional processes for producing a dialkyl carbonate by reacting urea or alkyl carbamate with alcohol, a high reaction temperature of 180.degree. C. or above and a reaction time of 8 hours or above were necessitated. The dialkyl carbonate which can be produced by the above-mentioned processes has been limited to the case used a high boiling point alcohol as the raw material. That is, when dialkyl carbonate is synthesized from both alcohol having a boiling point of 180.degree. C. or below and alkyl carbamate, it has been necessary to conduct the reaction for a very long time or to apply a pressure in order to ensure sufficient reaction temperature since sufficiently high reaction temperature cannot be ensured due to low boiling point of alcohol.
Japanese Patent Kokai (Laid-open) No. 57-26645 discloses a process for producing a dibutyl carbonate by using both butyl carbamate and butanol as raw materials. In the process, the reaction was carried out under the condition of an applied pressure of 9 to 10 bars, but the conversion rate of carbamate after 7 hours stayed to 40%. When isobutanol was used, 40 hours were necessary to complete the reaction, so that practical reaction rate could not be obtained.
Further, when the reaction is carried out under an applied pressure, the reaction apparatus becomes complicated and requires a high cost since produced ammonia must be removed while maintaining pressure.